U.S. mobile users bought fewer phones in the second quarter compared to last year, according to NPD Group, indicating the economic slowdown is affecting decisions to buy phones.

Mobile sales to consumers in the U.S. totaled 28 million devices in the second quarter, a 13 percent decline compared with the same period last year, NPD said.

People who did buy phones were more apt to buy devices traditionally reserved for business users. Of the handsets sold in the quarter, 28 percent of them had a full Qwerty keyboard, compared with 12 percent last year, NPD found.

Smartphones made up 19 percent of all mobile phone sales in the quarter, up 9 percentage points from the second quarter last year.

Phone buyers in the second quarter paid more than those who bought in the same quarter last year, but less than people who bought phones in the first quarter this year. The average selling price in the second quarter was US$84, up 14 percent compared with last year but down almost 4 percent compared with the previous quarter, according to NPD.

The researchers also found that people most often buy phones from stores operated by carriers, rather than mass merchandisers or electronics specialty stores.

Despite continuing to lose market share, Motorola has just managed to hang on to its leading position in the U.S. for the quarter. Of the phones sold, 21 percent were from Motorola, 20 percent from Samsung, 20 percent from LG, 9 percent from Nokia and 7 percent from Research In Motion. Around the world, those positions vary widely by geographic region, with Nokia maintaining the world's number one spot.